1. Field of Invention
The present invention relates to a method for determining malfunction of a nitrogen oxide sensor, and a selective catalytic reduction system.
2. Description of the Related Art
A typical selective catalytic reduction system cleans nitrogen oxide from a factory exhaust pipe by spraying a urea solution onto it. Recent research has addressed applying such a system to vehicle exhaust pipes.
When using such a system, the amount of nitrogen oxide in exhaust gas needs to be measure, usually by mapping or modeling. This poses a problem in vehicles, since the amount of nitrogen oxide changes with driving conditions or other catalyst devices.
To test malfunction of a nitrogen oxide sensor, using only output signals of the sensor is inaccurate. If driving parameters (such as fuel injection amount) are changed at random to test the sensor, noise, power fluctuation, and smoke are generated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.